The press conference began on the east lawn of the Capitol building at 9 a.m. Wednesday morning. King's office said it would last until 5 p.m., with a two-hour break from noon-2 p.m. The Washington Post's Ed O'Keefe estimated a crowd of about 300 showed up for the start of the rally.

"Border security, Rule-of-Law [favoring] Members of Congress are unlikely to get a full debate inside the halls of Congress," King said. "So we are taking the debate outside its halls."

But King made it clear that he was holding the rally in an attempt to stall the Senate's advancement on the bill.

"Now that the die is cast in the Senate, I think it’s useful to let folks know what you think — and maybe there’s a way to yet kill this thing in the Senate," King said, according to the Washington Post.

At a meeting of influential conservatives in New York last month, King said that his preferred immigration bill he would institute some kind of "point system" for immigrants, to "score" people by age, education, earning capability, language skills, and capital. He also praised the E-Verify system, an online tool that checks workers' immigration status.

Two weeks ago, King sponsored an amendment that Republicans in the House of Representatives moved to pass — one that would end policies of discretion for the Department of Homeland Security to delay deporting unauthorized young and other "low priority" immigrants.